1. Field of the Invention
This invention relates to an arrangement of a plurality of elementary transformers for impedance transformation which can be used as line transformers.
2. Description of the Related Art
In radio frequency technology, line transformers are used for broadband matching of two impedances which have a ratio of 1:2, for example, for matching two 50 ohm radio antennas which are connected in parallel to a 50 ohm transmitter and particularly for matching two transmission and reception antenna systems of a nuclear magnetic resonant tomograph system to one transmitter or, respectively, to one receiver. An arrangement of elementary transformers is provided for impedance matching so as to achieve an adequate bandwidth and obtain low transit losses.
Transformers suitable for the range of low frequency alternating current generally contain a core of magnetic material as well as a primary winding and a secondary winding each of which has at least a few turns. The quadrapole that is thus formed should modify current and voltage in the desired manner so as to accomplish an impedance transformation. Such transformers are suitable for impedance transformation as long as the length of the conductor forming one winding is short relative to the wavelength. As is well known, radio antennas should also transmit electromagnetic energy such as arbitrary signals which are undistorted and extremely high frequencies also. In broadband transformers, both windings are therefore so tightly coupled that they form lines having defined characteristic or image impedance and negligible radiation losses. In a practical manner, any rational transformer ratio can be realized with line transformers. A transformation ratio of 3:2 is obtained, for example, using five elementary transformers which have a transformer ratio of 1:1 with the first two transformers connected in parallel on the primary side and are secondarily connected in series. A voltage ratio of 1:2 is thus obtained. The three additional elementary transformers are connected in series on the primary side and are secondarily connected in parallel. A voltage transformation of 3:1 is thus obtained and a total transformation of 3:2. So as to obtain a transformation ratio of, for example, N:M however, the sum of N+M transformers has always been required as discussed in the publication NTZ 1966, No. 9, Pages 527-538. See also U.S. Pat. No. 4,095,163, U.S. Pat. No. 3,370,257, U.S. Pat. No. 3,428,886, British Patent No. 1,599,557, British Patent No. 2,161,940 and European Patent No. 129,464.